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PubMed2005

Interaction of task readiness and automatic retrieval in task switching: negative priming and competitor priming.

When subjects switch between tasks, performance is slower after a task switch than after a task repetition, even when preparation time is long. We report two experiments that support the idea that a large part of these residual task shift costs can be due to stimulus-cued retrieval of previous task episodes. We demonstrate that there are two different factors at work: (1) facilitation of response to the current distractor stimulus, appropriate to the previously relevant, competing task (competitor priming), and (2) impaired processing of previously suppressed responses (negative priming). Negative priming was contingent on the size of the stimulus set, suggesting that distractor suppression comes into effect only if the distractors are highly activated. Importantly, both types of interference interacted with task readiness: Whereas in the nondominant task (picture naming), switch and nonswitch trials were equally affected, the dominant task (word reading) showed priming effects on switch trials only. Thus, the retrieval of previous processing episodes has a selective impact on situations in which task competition is high.

Adult↗
PubMed2007

Juvenile hormone III influences task-specific cuticular hydrocarbon profile changes in the ant Myrmicaria eumenoides.

We investigated the influence of juvenile hormones (JH) on the composition of cuticular hydrocarbons (CHCs) and the division of labor in colonies of the African ant Myrmicaria eumenoides. CHCs have long been implicated in nestmate recognition in social insect colonies. In M. eumenoides, the CHC profiles also vary with the task performed from brood-tender-type to forager type. The endocrine factors regulating the task allocation as well as the intracolonial recognition cues are not well understood, but JHs are prime candidates. Only JH III was identified in the hemolymph of M. eumenoides workers. Foragers had significantly higher JH III titers than brood tenders. The application of exogenous JH III and a JH analogue (methoprene) to M. eumenoides workers did not result in an observable acceleration of task change in our study. However, longevity of the focus workers, and thus the observational period, was reduced by the applications. Changes from a brood-tender-type to a forager-type CHC profile were accelerated by the application of JH III and methoprene, resulting in brood-tending workers that displayed forager-type CHC profiles. We present the first data supporting that recognition cues of an eusocial Hymenopteran are influenced by JH III, which could thus play a major role in the regulation of the dynamic nature of social insect colonies. JH III is connected to at least two key processes: the acceleration of CHC changes and the more long-term modulation of task shifting. Moreover, this indicates that changes in CHC recognition cues do not trigger task allocation in social insect colonies.

Animals↗
PubMed1996

Vernier in motion: what accounts for the threshold elevation?

Vernier acuity is susceptible to degradation by image motion. The purpose of this study was to determine to what extent vernier thresholds are elevated in the presence of image motion because of reduced stimulus visibility, due to contrast smearing, or to a shift in the spatial scale of analysis. To test the visibility hypothesis, we measured vernier thresholds as a function of stimulus velocity (0-6 deg/sec), for various levels of stimulus visibility, each normalized to the detection threshold at the respective velocity. Contrary to the prediction of the visibility hypothesis, vernier thresholds worsen as the velocity increases, even when the stimuli are equally visible. To test the shift in spatial scale hypothesis, we determined spatial frequency tuning functions for vernier discrimination and line detection tasks, using a masking paradigm. We measured vernier and line detection thresholds as a function of spatial frequency of a sine-wave mask (0.5-32 c/deg), and for stimulus and mask velocities ranging from 0 to 4 deg/sec. Peak masking for both vernier discrimination and line detection, which indicates the most sensitive band of spatial frequencies for each task, shifts systematically toward lower spatial frequencies as the velocity increases. The progressive increase in spatial scale largely accounts for the worsening of vernier thresholds for moving stimuli. Differences between peak masking for vernier discrimination and line detection were found at 0 and 1 deg/sec, suggesting that different mechanisms mediate the two tasks, at least at low velocities. The masking results are consistent with previous findings that directionally selective motion detectors mediate detection of moving stimuli, but suggest that these detectors do not analyze vernier offsets. We conclude that the elevation of vernier threshold for a moving stimulus is accounted for primarily by a shift of sensitivity to mechanisms of lower spatial frequency, and not by decreased stimulus visibility.

Contrast Sensitivity↗
PubMed2005

Cognitive impairment in aged rhesus monkeys associated with monoamine receptors in the prefrontal cortex.

The "frontal aging hypothesis" has been proposed by many researchers suggesting that the earliest and most severe age-related changes in the cortex occur in the frontal lobes. Two of these changes include decreases in cognitive functions mediated by the prefrontal cortex (PFC) and significant decreases in norepinephrine (NE) and dopamine (DA). To investigate whether the changes in these neurotransmitter systems are directly related to the cognitive decline seen in aging we utilized the rhesus monkey as a model of normal human aging. Our goal was to determine if age-related changes in cognition is associated with changes in norepinephrine and dopamine receptor binding density in the PFC. Eight young monkeys between five and ten years of age (six males and two female) and eight aged monkeys between 25 and 32 years of age (five males and three females) were behaviorally characterized. Subsequently on-the-slide in vitro binding assays were used to quantify the alpha-1 adrenergic, alpha-2 adrenergic and DA1 receptors as well as the NE and DA uptake receptors. Aged animals as a group demonstrated significant cognitive impairments and aging produced a significant decrease in alpha-1 adrenergic and alpha-2 adrenergic receptor binding in the PFC but no significant change in binding for the DA1 receptor or the NE or DA uptake receptors. Further analysis revealed a significant relationship between monoamine receptor binding and cognitive performance on three tasks: delayed non-matching to sample, delayed recognition span test and the conceptual set-shifting task.

Adrenergic alpha-Agonists↗
PubMed2005

Learning and transfer of an ipsilateral coordination task: evidence for a dual-layer movement representation.

The present study addressed the nature of the memory representation for interlimb coordination tasks. For this purpose, the acquisition of a multifrequency (2:1) task with the ipsilateral limbs and transfer to the ipsilateral and contralateral body side was examined. In particular, subjects practiced a 2:1 coordination pattern whereby the right arm moved twice as fast as the right leg, or vice versa. Subsequently, they transferred the practiced 2:1 task to three different conditions: (1) the converse partner (i.e., the slow-moving limb had to move fast, and vice versa) at the ipsilateral body side, and (2) the identical and (3) converse 2:1 pattern at the contralateral body side. Findings revealed positive transfer of the identical and converse 2:1 pattern to the contralateral body side. However, no transfer of the learned pattern to its converse partner at the same body side was revealed. We propose a new memory representation model for coordination patterns, composed of an effector-independent and effector-specific component (dual-layer model). It is hypothesized that the general movement goal (i.e., moving one limb twice as fast as the other) constitutes the abstract, higher-level representation that may account for positive contralateral transfer. Conversely, the effector-specific component contains task-specific lower-level muscle synergies that are acquired through practice, prohibiting positive transfer when shifting task allocation within the same effectors. These findings are consistent with recent neuroscientific evidence for neuroplastic changes in distributed brain areas.

Adult↗
PubMed2004

Simulator sickness when performing gaze shifts within a wide field of view optic flow environment: preliminary evidence for using virtual reality in vestibular rehabilitation.

BACKGROUND: Wide field of view virtual environments offer some unique features that may be beneficial for use in vestibular rehabilitation. For one, optic flow information extracted from the periphery may be critical for recalibrating the sensory processes used by people with vestibular disorders. However, wide FOV devices also have been found to result in greater simulator sickness. Before a wide FOV device can be used in a clinical setting, its safety must be demonstrated. METHODS: Symptoms of simulator sickness were recorded by 9 healthy adult subjects after they performed gaze shifting tasks to locate targets superimposed on an optic flow background. Subjects performed 8 trials of gaze shifting on each of the six separate visits. RESULTS: The incidence of symptoms of simulator sickness while subjects performed gaze shifts in an optic flow environment was lower than the average reported incidence for flight simulators. The incidence was greater during the first visit compared with subsequent visits. Furthermore, the incidence showed an increasing trend over the 8 trials. CONCLUSION: The performance of head unrestrained gaze shifts in a wide FOV optic flow environment is tolerated well by healthy subjects. This finding provides rationale for testing these environments in people with vestibular disorders, and supports the concept of using wide FOV virtual reality for vestibular rehabilitation.

Journal Article↗
PubMed2006

Acute neuropsychological effects of methylphenidate in stimulant drug-naïve boys with ADHD II--broader executive and non-executive domains.

BACKGROUND: Accumulating evidence supports methylphenidate-induced enhancement of neuropsychological functioning in attention deficit hyperactivity disorder (ADHD). The present study was designed to investigate the acute effects of the psychostimulant drug, methylphenidate (MPH), on neuropsychological performance in stimulant naïve boys with ADHD. METHODS: Seventy-three drug-naïve boys (age 7-15) with ADHD (combined type) completed neuropsychological tasks from the CANTAB battery under randomised, placebo controlled, double-blind conditions following an acute challenge with either placebo (n = 24), .3 (n = 25) or .6 (n = 24) mg/kg oral MPH. RESULTS: MPH did not impair performance on any task. MPH (.6 mg/kg) lengthened response latencies on a task of Spatial Recognition, shortened response times on a Reaction Time task and restored performance on a Delayed Matching to Sample visual, non-working memory task. Contrary to predictions, MPH did not enhance performance on tasks with a prominent executive component, including Go/NoGo, Spatial Working Memory, Stockings of Cambridge and Attentional Set shifting tasks. CONCLUSIONS: Acute administration of MPH to drug-naïve boys with ADHD did not impair neuropsychological performance. Acute MPH enhanced performance on some aspects of non-executive functioning. MPH-induced slowing of responding on a relatively complex Spatial Recognition memory task and quickened responding on a reaction time task requiring less cognitive resources suggests that MPH may act by improving self-regulatory ability. MPH may not exert its effects on neuropsychological functioning by enhancing executive processes.

Adolescent↗
PubMed2006

Cue-based preparation and stimulus-based priming of tasks in task switching.

In this study, we investigated the interaction of three different sources of task activation in precued task switching. We distinguished (1) intentional, cue-based task activation from two other, involuntary sources of activation: (2) persisting activation from the preceding task and (3) stimulus-based task activation elicited by the task stimulus itself. We assumed that cue-based task activation increases as a function of cue-stimulus interval (CSI) and that task activation from the preceding trial decays as a function of response-stimulus interval Stimulus-based task activation is thought to be due to involuntary retrieval of stimulus-associated tasks. We manipulated stimulus-based task activation by mapping each of the stimuli consistently to only one or the other of the two tasks. After practice, we reversed this mapping in order to test the effects of item-specific stimulus-task association. The mapping reversal resulted in increased reaction times and increased task shift costs. These stimulus-based priming effects were markedly reduced with a long CSI, relative to a short CSI, suggesting that stimulus-based priming shows up in performance principally when competition between tasks is high and that cue-based task activation reduces task competition. In contrast, lengthening the response-cue interval (decay time) reduced shift costs but did not reduce the stimulus-based priming effect The data are consistent with separable stimulus-related and response-related components of task activation. Further theoretical implications of these findings are discussed.

Adult↗
PubMed1979

The utilization of external and movement cues in simple spatial tasks by blind and sighted children.

The role of visual experience in coding spatial position by movements or by external cues was examined in simple (nonrotational) shift tasks with blind and sighted children. Age and the salience of external cues were also of interest. Results showed that the congenitally totally blind used movement cues significantly more even when external cues were present and prominent. The blind with minimal visual experience coded by external cues, but made errors beyond the age by which blindfolded sighted children performed correctly. It was argued that visual experience affects coding by drawing attention to external cues, and by providing more adequate spatial information than other sources usually available to the blind. In its absence, movement coding and self-reference can become preferred strategies.

Adolescent↗
PubMed1980

[Discrimination shift learning and dimensional dominance in mental retarded children (author's transl)].

Dimensional dominance (either form or color) among retarded and normal children was assessed prior to their being presented with reversal or nonreversal shift task. During the initial learning, the dominant dimension was either relevant or irrelevant to the solution. Both rate of criterion attainment during the initial learning and subsequent shift performance were related to dimensional dominance. If the dominant dimension was relevant, the retarded learned the task as fast as the normal; if the dominant dimension was irrelevant, the retardates learned it with more difficulty than the normals. This result was discussed in relation to the tendency of the retardates' towards being bound to one dimension and no switching to an other.

Child↗
PubMed2005

Cognitive biases toward alcohol-related words and executive deficits in polysubstance abusers with alcoholism.

AIM: To study cognitive biases for alcohol-related cues on executive function tasks involving mental flexibility and response inhibition in polysubstance abusers with alcoholism. DESIGN: The responses to alcohol-related cues of detoxified polysubstance abusers with alcoholism and of non-addicts were compared. SETTING: The University of Iowa City, Iowa, USA. PARTICIPANTS: Thirty detoxified polysubstance abusers with alcoholism (PSA) and 30 healthy non-substance abusers (CONT). MEASUREMENTS: Using the 'Alcohol Shifting Task', a variant of the go/no-go paradigm, we measured the response times and the accuracy of responses to targets and distracters. Sometimes the alcohol-related words were the targets for the 'go' response, with neutral words as distracters, sometimes the reverse. Several shifts in the type of the target occurred during the task. FINDINGS: Relative to CONT, PSA were generally slower to respond to targets, but the group difference was smaller when alcohol-related words were the targets. A signal detection analysis also indicated that relative to CONT, the PSA had more difficulties discriminating between targets and distracters (low d'), and they showed more signs of decision bias (low C), reflecting increased readiness to respond to both targets and distracters. However, these discrimination and inhibition deficits were more pronounced when alcohol-related words were the targets. Furthermore, the weaknesses in RT and C were more pronounced in PSA after shifting the targets from alcohol-related to neutral words, or vice versa. CONCLUSIONS: These results suggest that PSA have cognitive biases towards information related to alcohol, and that these biases, as well as the poor executive functions (lower mental flexibility and response inhibition) revealed in PSA might be responsible for their failure to maintain abstinence.

Adult↗
PubMed1999

Comparison of set-shifting ability in patients with chronic schizophrenia and frontal lobe damage.

Neuropsychological studies of patients with schizophrenia have consistently identified deficits on tests sensitive to frontal lobe function. One paradigm that has been widely used is that of attentional set-shifting using the Wisconsin Card Sorting Test (WCST). In the present study, patients with chronic schizophrenia and with frontal lobe lesions were assessed on a computerised set-shifting task that provides a componential analysis of the WCST by distinguishing between intra-dimensional and extra-dimensional set-shifting. Out of 51 patients with schizophrenia, those with high IQ (n =24) were compared with patients with lesions in prefrontal cortex (n = 22) and with normal control subjects (n= 18). These three groups were well matched for age, sex and National Adult Reading Test (NART) IQ. The schizophrenic group showed a significantly higher rate of attrition at the intra-dimensional shift stage of learning compared with the other two groups. At the extra-dimensional shift stage, both the schizophrenic and frontal lesioned groups showed greater attrition than controls. Further, patients with schizophrenia who were able to learn the intradimensional reversal stage required more trials and made significantly more errors at that stage than the other two groups. In comparison with high IQ patients with schizophrenia, those with low IQ performed at a lower level but showed a qualitatively similar pattern of performance, providing further evidence that the set-shifting deficits were not simply explained by any global intellectual decline. Patients with schizophrenia who dropped out at the extradimensional shift stage had higher negative symptom scores compared with patients dropping out at previous learning stages, while patients failing at the intra-dimensional shift stage had lower scores for bradyphrenia (slowness of thought). The results suggest that patients with chronic schizophrenia fail to 'learn set' and are impaired at both set-shifting and concept formation. The relevance of these findings to understanding the nature of prefrontal cortical deficits in chronic schizophrenia is discussed. The implication of these findings to the rehabilitation of these patients is considered.

Adult↗
PubMed2003

Prefrontal neuronal activity encodes spatial target representations sequentially updated after nonspatial target-shift cues.

We examined prefrontal neuronal activity while monkeys performed a sequential target-shift task, in which, after a positional cue indicated the initial saccade target among 8 peripheral positions, the monkeys were required to internally shift the target by one position on every flash of a target-shift cue. The target-shift cue appeared in the center 0 to 3 times within a single trial and was always the same in shape, size, and color. We found selective neuronal activity related to the target position: when the target-shift cue implied the target shift to particular peripheral positions, neurons exhibited early-dominant and late-dominant activity during the following delay period. The early-dominant target-selective activity emerged early in the delay just after the presentation of the target-shift cue, whereas the late-dominant activity gradually built up toward the end of the delay. Because the target-shift cue was not related to any specific target location, the early-dominant target-selective activity could not be a mere visual response to the target-shift cue. We suggest that the early-dominant activity reflects the transitory representation for the saccade target that was triggered by the nonspatial target-shift cue, whereas the late-dominant activity reflects the target representation in the spatial working memory or the preparatory set for the possible impending saccade, being repeatedly updated during sequential target shifts.

Animals↗
PubMed2004

Dyslexics show a deviant lateralization of attentional control: a brain potential study.

The present study compared performance and event-related brain potentials between dyslexic subjects and control subjects while they performed a spatial selective attention-shifting task. The subjects received a prestimulus cue on each trial, which indicated whether the subjects should attend to a position to the left of fixation or to the position at the opposite right of fixation. Thereafter a stimulus was presented either at the cued position or at the other position. In this paper we report on the brain activity in the cue-stimulus interval, which is supposed to reflect processes involved in controlling spatial attention shifting. The dyslexics performed much poorer on this task than the control subjects. The ERP-effects of cue direction closely resembled earlier reports, and consisted of an early (onset at about 200 ms) posterior contralateral negativity, a later (onset at about 350 ms) posterior contralateral positivity, and a later (onset at about 350 ms) frontal positivity. Dyslexics and controls differed with respect to the frontal attention effect. Whereas the controls showed this effect almost exclusively over the right hemisphere, the dyslexics showed both left and right hemispheric effects. We propose that this might support the idea that in dyslexia the development of interhemispheric asymmetry is disregulated.

Adult↗
PubMed2000

Profiles of cognitive dysfunction in chronic amphetamine and heroin abusers.

Groups of subjects whose primary drug of abuse was amphetamine or heroin were compared, together with age- and IQ-matched control subjects. The study consisted of a neuropsychological test battery which included both conventional tests and also computerised tests of recognition memory, spatial working memory, planning, sequence generation, visual discrimination learning, and attentional set-shifting. Many of these tests have previously been shown to be sensitive to cortical damage (including selective lesions of the temporal or frontal lobes) and to cognitive deficits in dementia, basal ganglia disease, and neuropsychiatric disorder. Qualitative differences, as well as some commonalities, were found in the profile of cognitive impairment between the two groups. The chronic amphetamine abusers were significantly impaired in performance on the extra-dimensional shift task (a core component of the Wisconsin Card Sort Test) whereas in contrast, the heroin abusers were impaired in learning the normally easier intra-dimensional shift component. Both groups were impaired in some of tests of spatial working memory. However, the amphetamine group, unlike the heroin group, were not deficient in an index of strategic performance on this test. The heroin group failed to show significant improvement between two blocks of a sequence generation task after training and additionally exhibited more perseverative behavior on this task. The two groups were profoundly, but equivalently impaired on a test of pattern recognition memory sensitive to temporal lobe dysfunction. These results indicate that chronic drug use may lead to distinct patterns of cognitive impairment that may be associated with dysfunction of different components of cortico-striatal circuitry.

Adolescent↗
PubMed2006

Dissociating neural indices of dynamic cognitive control in advance task-set preparation: an ERP study of task switching.

Switching between different tasks is associated with performance deficits, or 'switch costs', relative to repeating the same task. Recent evidence suggests that response rather than task selection processes may be a major cause of switch costs [Schuch, S., Koch, I., 2003. The role of response selection for inhibition of task sets in task shifting. J Exp Psychol Hum Percept Perform, 29 (1) 92-105]. Thus, switch costs are not incurred if on the preceding trial a task has been prepared for but no response required (a 'no-go' trial). We investigated the relationship between response selection and the subsequent preparation of an alternative task set. While switch costs were absent following 'no-go' trials, ERP differences during the precueing interval showed that response selection has implications for subsequent task preparation as well as for task performance per se. The results are discussed in relation to the dissociation of intention versus action in behavioural control and the role of inhibition in switching between task sets.

Adult↗
PubMed2006

Thalamic-prefrontal cortical-ventral striatal circuitry mediates dissociable components of strategy set shifting.

The mediodorsal nuclei of thalamus (MD), prefrontal cortex (PFC), and nucleus accumbens core (NAc) form an interconnected network that may work together to subserve certain forms of behavioral flexibility. The present study investigated the functional interactions between these regions during performance of a cross-maze-based strategy set-shifting task. In Experiment 1, reversible bilateral inactivation of the MD via infusions of bupivacaine did not impair simple discrimination learning, but did disrupt shifting from response to visual cue discrimination strategy, and vice versa. This impairment was due to an increase in perseverative errors. In Experiment 2, asymmetrical disconnection inactivations of the MD on one side of the brain and PFC on the other also caused a perseverative deficit when rats were required to shift from a response to a visual cue discrimination strategy, as did disconnections between the PFC and the NAc. However, inactivation of the MD on one side of the brain and the NAc contralaterally resulted in a selective increase in never-reinforced errors, suggesting this pathway is important for eliminating inappropriate strategies during set shifting. These data indicate that set shifting is mediated by a distributed neural circuit, with separate neural pathways contributing dissociable components to this type of behavioral flexibility.

Animals↗
PubMed1989

Comparison of accommodative adaptation using laser and infra-red optometers.

Previous investigations have reported differences in the rate of decay of accommodative adaptation depending on the form of optometer used to assess dark-focus (DF). This study has used both laser and infra-red optometers to measure pre- and post-task values of DF in 10 subjects. DF was assessed before and immediately after an 8 min near-vision task performed at the subjective near-point of accommodation. Examination of the data from the two optometers revealed significant differences in both magnitude and distribution of pre-task DF. Additionally variations in the post- to pre-task shift in DF were observed between the two methods of assessment. Using the laser optometer, six subjects exhibited positive adaptation following the near-task which was not apparent with the infra-red optometer. The data suggest that both instruments may not be sampling open-loop accommodation; the laser optometer is particularly vulnerable to extraneous influences.

Accommodation, Ocular↗